the onboard buffer preamp is used for the line driving capabilities from the guitar to the next device, either the amp or effects. it should be placed as closest to the pickups as possible. if you are going to use it right at the jack of the guitar, i would believe this to be the better option at getting close to that criteria. but on the floor is a waste of effort as the line going to it still will have a capacitance/resistance interaction especially with longer cables. i know they make some pretty superb cables these days, but they have not eliminated the capacitance/resistance factor yet. so there will still be the ever so slight tone adjustment of even the best cables. if you run effects in a traditional inline manner, and even one of them is not true bypass, you are already running a buffer or line driving preamp right there. sometimes though with multiple effects buffers run together you get an even more degradation of tone as the buffers mingle with themselves.
i'd definately consider running one onboard the guitar, and i am not self promoting my preamp, there are a ton out there, the cae's, emg's and even the DIY types. splicing something in there with a battery is definately worth a trial period to see/hear the benefits of what it does. even if it is in a temporary status.
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